The objective of this study is to test the toxicity and efficacy of whole body hyperthermia (WBH) given in combination with radiation in dogs with naturally occurring intracranial neoplasms. If hyperthermia combined with radiation is to be clinically useful for treatment of solid tumors the tumor response must be greater than the response of the surrounding normal tissue. Of particular interest is the response of slowly proliferating normal tissues which have been perturbed by the presence of the tumor. Little information is available on this important response to cancer therapy with heat and radiation. In this study it will be possible to compare the response of the canine brain tumor bed to radiation alone and radiation combined with WBH. In addition the response of naturally occurring intracranial neoplasms in dogs to radiation alone and radiation combined with WBH will be determined in the same animals. For radiation therapy, the sensitivity of late responding tissue frequently limits the total dose that can be used. This is particularly true of brain tumors where response of the tumor bed and surrounding normal tissue determine the total dose that can be used. Hyperthermia may enhance the response of tumor more than the response of the tissues of the tumor bed and therefore lead to a therapeutic gain for the combination of irradiation and hyperthermia. To provide a more uniform hyperthermic treatment, total body hyperthermia will be used for which temperatures of approximately 42degreesC can be achieved. Clinical, electrophysiologic, CT, and morphometric histologic evaluations will be done.